The background estimate and removal was performed by using the photutilshttps://photutils.readthedocs.io/en/stable/background.html package ([1]}). We estimated a 2D median background, by dividing the field of view into boxes and substituting the pixel intensities in each box with the median background for that box. This generated a low-resolution background which was subtracted from the image. The box size was estimated to remove as much background as possible but avoiding any source removal, including the PSF sidelobes. The box size, the width of the Gausian smoothing function, and the error in the PSF scale-factorThe actual value of the scale factor is unimportant, since it depends on the normalisation of the PSF, which is arbitrary are given in Table REF . The images of the CS and its immediate surroundings with the A2V star subtracted, for the same set of selected filters as in Fig. REF , are shown in Fig. REF . Most of the negative residuals in these images lie relatively close to the sharp diffraction structures and most likely are a result of inherent limitations in the PSF simulator tool's ability to reproduce the observed PSF.
